The vehicle information and communication system (VICS) is known as a conventional service for broadcasting traffic information. The present service is implemented to provide various kinds of traffic information and vehicle information to a user. For example, the VICS Center is caused to transmit traffic information, such as traffic congestion information about the road, to a vehicle. In addition, a vehicular device is caused to search map data for identifying a road. Furthermore, a display device is caused to change a display mode of a road according to the received traffic information. The present service enables a user to obtain traffic information such as traffic congestion information in real time.
A vehicular device stores map data including road data in a format defined with links and nodes. A link represents a road having nodes being termination points. The VICS Center transmits the VICS Link being information for identifying roads. The VICS link is assigned with various traffic information and change instruction information on a display mode. A vehicular device has a position reference table for comparing the VICS Link with links in the map data. The vehicular device searches a link corresponding to the VICS Link with reference to the table. That is, the position reference table is requisite for the VICS system (see, for example, JP-A-2006-275777 and JP-A-2009-270953).
As an alternative service to the VICS system, it is conceived to utilize data of traffic information transmitted in the form of transport protocol expert group (TPEG) to a terminal device such as a vehicular device. It is noted that in the case of TPEG data being transmitted, position information is represented in the form of, for example, dynamic location referencing data (DLR data). The position information includes core points each having position coordinates and attributes for identifying a road. In general, the core point is distributed in the form of multiple arrays arranged along the road. In the system where the core points are used to represent position information, a position reference table, which may vary in dependence upon difference in manufacturer of the map data, the format and the version of the map data, and the like, is unnecessary. That is, the system using the core points enables identification of a road (link) on the map data, regardless of the map data in the vehicular device.
To the contrary, the system using the core points needs various processings for identifying a road according to the core points. For example, as described above, various kinds of map data exist. Therefore, core points do not necessarily exist on a road of map data. Therefore, it is necessary to implement a processing to identify a link pertinent to a road represented by core points on a map.
The map data is managed in the unit of divided region being one of multiple areas. The multiple areas are formed by dividing the map data into multiple sections. The divided region is called a parcel. For example, when a map is indicated, processings are implemented in the unit of the divided region. Therefore, for example, in the case where a road extends beyond the divided region, the termination points, such as nodes, of a link corresponding to the road of the map data are certainly assigned in the boundary of the divided region, in consideration of necessity in the processes.
Core points being distributed are multiple arrays arranged along a road. In general, core points are located beyond the boundary of the divided region of the map data. A termination point of a link, which is assigned for convenience as described above, corresponding to a core point may exist on the boundary by chance. Nevertheless, in general excluding such a case, a core point corresponding to the termination point of the link assigned in the boundary of the divided region does not exist. As a result, it may be difficult to identify a link, which is pertinent to the road represented by the core points, in the divided region.